IE50094B1 - Process for the treatment of solutions of lead chloride - Google Patents

Abstract

A process for the treatment of solutions of lead chloride, containing as impurities at least one metal chosen from the group consisting of silver, copper and bismuth. This process is characterized by the fact that it involves the following steps: (a) bringing the solution into contact with a cation exchange resin whose active group is a sulfhydryl group; and (b) recovery of the lead on the basis of the solution obtained in step (a).

Description

The object of this invention is a process for the treatment of solutions of lead chloride containing as impurities at least one metal chosen from the group consist ing of silver, copper and bismuth.

It involves more particularly a technique of elimination of the last traces of silver, copper and bismuth contained in solutions of lead chloride.

During the last five years, numerous methods have been proposed to recover the lead contained in different lead-bearing materials, such as oxidized and sulfurized minerals, as well as waste and residues of metallurgical treatment plants, methods which utilize the relatively high solubility of lead when it is in the form of chloride in a brine of alkaline or alkaline earth metals or of ammonium chloride.

Even when the mineral is very pure it contains in the impurity state other elements of which the most troublesome are silver, copper and bismuth. These metals, in the dissolution of lead, behave in general like the latter, are equally dissolved, and constitute impurities in the solution.

There exist numerous methods for eliminating impurities of lead chloride in solution. Among these methods can be mentioned cementation using metallic lead, sulfur -2precipitation using galena as presented in the French specification No. A-2 359211, submitted by the applicant, and crystallization.

The former two do not make it possible to obtain solutions of lead chloride which are completely rid of silver, copper and bismuth. The efficiency of these methods being limited by the thermodynamic equilibria, it is not possible to increase it. Crystallization, on the other hand, makes it possible to obtain lead chloride of very high purity. However, this technique uses a great deal of energy since it involves a reduction of several tens of degrees centigrade of the lead chloride solution to precipitate the latter, the redissolution in a heated state of the lead chloride precipitated, and the reheating of the initial lead chloride solution. This is the reason why it is used with reluctance at the industrial level.

This is why one of the objects of the present invention is to provide a process of purification of lead chloride solutions which makes it possible to eliminate almost all the silver, copper and bismuth present in this solution, and notably to lower the ratios of silver/lead, copper/ lead and bismuth/lead to a level below 10 ppm.

Another object of the present invention is to furnish a process of the type above which does not consume a great deal of energy. 30094 -3These objects, as well as others which will appear below, are attained by a process for the treatment of lead chloride solutions containing as impurities at least one metal chosen from the group consisting of silver, copper and bismuth, characterized by the fact that it involves the following steps: (a) bringing the solution into contact with a cation exchange resin whose active group is a sulfhydryl group; and (b) recovery of the lead on the basis of the solution obtained in step (a).

The sulfhydryl (-SH) group may be selected from one of th following functi onal groups: R1 1 -C-S-H; 1 S II -C-S-H; NH II -C-S-H <—> NH, 1 ά -C=S ; R -C-° . SH The present invention gives particularly good results and 20 is particularly well adapted to problems posed by lead chloride solutions whose composition is indicated in the following ranges, giving the usual range and the pre ferred range: Usual Range Preferred Range Chloride ions (Cl) 4 to 6 equivalent g/1 4 to 5 equivalent g/1 Lead 25 to 60 g/1 30 to 40 g/1 Ferrous ions 0 to 60 g/1 0 to 60 g/1 Zinc 0 to 30 g/1 0 to 20 g/1 Silver 0.1 to 200 mg/1 0.1 to 100 mg/1 Copper 0.2 to 2000 mg/1 0.2 to 200 mg/1 Bi smuth 0.1 to 200 mg/1 0.1 to 100 mg/1 pH 0 to 5 1 to 4 The sulfhydryl (-SH) particularly thiol groups, make possible by themselves the complete elimination of the silver and bismuth present in the solution, whereas the elimination of copper is subject to another parameter, which is the Redox potential of the solution. If the elimination of copper must be total, the copper must, as completely as possible, be in the cuprous form. Furthermore, the -SH groups present the disadvantage of being sensitive to oxidation.

The solutions resulting from oxidizing leaching of galenas XXX are in particular liable to contain traces of Fe ions and bivalent copper. These two compounds, particularly the Fe +++ ions, partially destroy the active group of the resin. For these reasons, it is appropriate before realizing the purification of step (a) to reduce the solution to bring the entirety of the copper to the cuprous form, the apparent oxide reduction potential being advantageously lower than or -5equal to 0, and preferably at -520 millivolts with regard to the saturated calomel electrode, this latter being in the same conditions as the solution.

The potential, however, must not be too reducing to prevent the precipitation of lead in the metal form from being too great.

Such a reduction can be effected by putting the lead chloride solution into contact with the galena, or preferably with the metallic lead. With this latter material, this technique presents the advantage of eliminating from the solution a large part of the silver, copper and bismuth in the form of cements, and therefore of being able to purify a larger quantity of solution per unit of volume of resin.

To obtain a still better result, one can bring the solution in the course of purification into contact with the metallic lead, in any manner, and thus maintain the solution's potential during the entire step (a) at a value, for example, between -520 and -560 millivolts in relation to the saturated calomel electrode at 60°C.

The reduction can be likewise effected by the electrolytic method. -6The temperature of the solution during step (a) is preferably located between 60°C and the boiling temperature.

For reasons of a practical nature, the pressure chosen is preferably atmospheric pressure. However, in certain cases pressures above or below atmospheric pressure can be used without altering the performance of the process.

The resins used in the course of step (a) can be, for example, resins sold under the commercial designation of IMACTI GT 73 by the Imacti Company and the resin sold under the commercial designation of LEWATIT OC 1014 by the Bayer Company. These two resins have as their active group the sulfhydryl group (-SH).

The solutions obtained after step (a) from the process according to the present invention have a silver, copper and bismuth content below the analytical detection limit; i.e., respectively below 0.1, 0.2 and 0.1 milligrams per liter.

Once the solution is purified, the lead can be recovered according to techniques already known,for example, by precipitating its salt, reducing it to the metallic state chemically or case-hardening it. However, one ofthe great advantages of purification according to the present invention is that it permits the direct acquisition of lead of high -7SQQSfi quality by electrolysis of the solution. Such electrolysis leads to the precipitation of lead whose purity can easily reach 99.95%, containing at the most 15 ppm of copper, ppm of silver and 20 ppm of bismuth, the electrolysis having a tendency to raise the ratios between the impurities and the lead.

Resins saturated with silver, copper and/or bismuth can be reclaimed in the following manner: (c) elution of the resin saturated with impurities 10 by a solution of hydrochloric acid whose normality is between and 12 N, preferably near 8 N.

When the active groups are altered by oxidation, they can be reclaimed by means of a solution of sodium sulfide.

The objective of the following nonrestrictive examples is 15 to put specialists in a position to determine easily the operative conditions which are suitable for use in each particular case.

Example 1 A solution is prepared which only contains chlorides of 20 the following composition: NaCl 250 g/1; Pb+2 30 g/1 ; -8Fe +2 20 g/1; Bi +3 50 mg/1; Ag + 10 mg/1; and Cu + 10 mg/1.

This solution is brought to the temperature of 90°C and continuously passed through two columns in series.

The first column contains lead turnings and effects a first purification by cementation of copper, silver and bismuth. Upon leaving this column, the solution contains less lOthan 0.1 mg/1 of bismuth and silver, but still 1 mg/1 of copper.

The second column contains an ion exchange resin sold under the trademark of LEWATIT OC 1014. Upon leaving this second column, the content of copper, silver and bismuth is below 15the analytical detection limit specified above, the mass ratio between these impurities and the lead being 7,3 and 3 ppm, respectively. An output of 10 B.V./hr is achieved for 50 hours without observing an escape of copper in the solution.

It is, however, important that the solution not be reoxidized between the two columns. It has been observed that when air remains in the filter located between the two columns, the purification obtained by the resin is much worse. One can conclude from this that the resin fixes the cupric ion less well than the cuprous ion. -950 09 4 The association of the cementation on the lead and of passage over resin containing -SH groups thus appears as an extremely efficient method for eliminating copper from a solution containing lead.

Example 2 Puri fi cati on The solution resulting from corrosion effected according to the technique described in French patent application No. 76-22.138, published under the number 2,359,211, is treated in an install ation fncluding a storage tank for the solution resulting from the corrosion and a cementation reactor. This cylindrical reactor is composed of two superposed parts separated by an inclined partition in the form of a funnel. The impure corrosion solution is admitted into the lower compartment where the lead electrolytic powder is kept in suspension, causing the cementation of noble metals. The roughly purified solution is drawn off by an overflow system, in the upper part, not agitated, without an important carrying away of the solid. The two compartments of the reactor have a volume perceptibly equal to 0.85 liters.

The installation also includes a column temperature controlled at 90°C furnished with ion exchange resin sold under the trademark IMACTI GT 73. The solution coming from the cementation reactor is introduced at the base of this column, after clarification. -10The operational parameters of the purification are: Delivery output: 0.85 liter/hour Volume of each cementation reactor compartment: 0.85 liter Volume of resin 1n the column: 0.085 liter Volume of treated solution: 30 liters The different phases produced during the purification operation correspond to the following chemical analysis: Element Pb 9/1 Cu mg/1 Ag mg/1 Initial solution 30.0 60 0.9 Solution after cementation 30.0 0.8 40.1 Solution passed through the resi n 30.0 40.2 40.1 The solution purified by the preceding step is then treated in an electrolysis installation. This installation includes: a storage tank of purified solution; and an electrolysis cell.

The pure solution of PbCl2 is pumped into the cathode compartment where it is rid of part of the lead which it contains before going through the diaphragm to penetrate the anode compartment. After oxidation of the ions of §009 4 -11Fe ++ to Fe +++, the anolyte is eliminated from the container. The lead formed is recovered, measured, then melted in the presence of soda at 400°C. The ingot obtained corresponds to the following chemical analysis: Element Cu PPm Ag PP® B.i ppm As ppm —5Έ- ppm Zn PPm Ingot 8 45 45 20 420 2 The quality of the product obtained is remarkable. Only a very small copper contamination is observed.

Example 3 The implementation of a complete process including: the selective corrosion of lead in a mixed concentrate of PbS, ZnS, and CuFeSgj rough purification of the corrosion solution by cementation with lead powder; fine purification with ion exchange resin; and production of ultra pure electrolytic lead by electrolysis of the solution purified.

The treated product is a mixed concentrate of PbS-ZnSCuFeS2, obtained by total flotation of solid pyrites of Aljustrel (Portugal). This product undergoes the following successive operations: (a) Selective dissolution of the lead. In a one liter reactor, a concentrate and mixed solution of FeClg-FeClg 50084 -12are introduced jointly and continuously in a medium of NaCl. The respective flows of solution and solid are chosen such thatthe ferric chloride is introduced in an amount slightly below stoichiometry in relation to the amount of galena present in the concentrate. The operative parameters with regard to this operation are the following: Flow 1.19 1/h Concentrate flow 627 g/h Temperature 90°C Concentration NaCl solution 250 g/1 Concentration Fe +++ initial solution 9.54 g/1 Concentration Fe initial solution 7.8 g/1 Concentration Pb ++ initial solution 10 g/1 Stoichiometry PbS/FeCl, 1.04 Q.S. (stoichio- metric quanti ty) (Reaction 2FeCl3 + IPbS + PbClg + 2FeCl2 + S°) Duration of the action 9 hrs., 30 mi ns.

The entering and existing phases corresponding to this experiment correspond to the following chemical analysis: Element Pb% 9/1 Zn% 9/1 Cu% 9/1 Fe 1 total ; Fe444 «9/1 i 9/1 Ag% 9/1 s% Initial concentrate 3.2 9.5 2.5 33.0 ; i 0.007 43.9 Initial solution 10 0 0 17.3 9.54 0 Hashed corrosion residue 0.27 10.1 2.68 36.0 ' 0.006 48.0 Solution resulting from the corrosion 25.2 2.02 0.038 18.5 ’ 0.02 1 0.007 This leaching has made it possible to dissolve the prin10 cipal elements in the following proportions: Lead: 92% Zinc: 2.7% Copper: 0.3% Iron: 0.2% Silver: 20% It is established that the dissolution of lead has been very selective relative to the other elements5 because the quantity of PbS is greater than the stoichiometric quantity preferably between 1.01 and 1.2 times the stoichiometric 20 quantity. (b) Purification of the lead solution. This operation has been effected in the equipment described in Example 2, including a two compartment cementation reactor and an ion exchange resin column.

The operative parameters concerning the purification in two steps are the following: Delivery rate: 0.85 Cementation reactor volume turbulent part: 0.85 calm part: 0.85 Resin bed volume: 0.085 During the purification, the eliminated impurities are distributed in the following manner: Phase Involved ^Distribution Copper Silver Bi smuth Cement 92 91 58 Resin 8 9 42 (c) Electrolysis of the solution after the resin. This operation has been effected in the installation and the conditions described in Example 2. The solution leaving the resin column is sent directly to the electrolysis bath. The operations of purification and electrolysis are in effect conducted jointly.

The lead collected after the electrolysis is washed, then melted at 400°C in the presence of soda. The resulting ingot has the following chemical analysis: -1530094 Element Cu Ag Bi Sb 1 As Zn Sn Concentration (ppm) 410 *•10 <10 4.100 f j x 40 4-10 4.100 This example illustrates perfectly the possibility of producing high purity metallic lead from any impure compound containing galena.

Example 4 Elution of IMACTI GT 73 resin with hydrochloric acid.

A series of experiments is conducted with columns maintained at 90°C by circulation of hot water in a double envelope.

Each experiment is effected in two cycles: (1) The resin is first saturated using a synthetic solution of copper chloride in sodium chloride, titrating about g/1 of copper. The resin thus saturated contains, according to experiments, from 60 to 80 g/1 of copper per liter. (2) Each of the resin portions is then rinsed with water to eliminate the impregnating solution. The elution operation is then performed, with aqueous solutions of hydrochloric acid of different normalities depending on the resin batch.

The elution solution is collected by fraction from a bed volume which will be designated as B.V. (Bed Volume), and -16a determination of the copper concentration is conducted for each fraction. It is thus possible to determine the proportion of copper eluted, as a function of the amount of elution solution collected, and depending on the various hydrochloric acidities.

Cumulative Number of Bed Volumes Collected Cumulative Percentage of Copper Collected Elution by HCl 3.95 N Elution by HCl 5.8 N Elution by HCl 6.8N Elution by NCI 7.6 N 1 2.1 3.1« 13.0 17.7 2 16.4 30.6« 54.9 70.0 3 27.0 50.6« 75.6 93.8 4 35.0 65.5« 88.4 98.7 5 41.4 77.2« 95.5 6 46.9 85.9« 97.0 7 51.44 92.2« 8 55.40 95.4« 9 58.90 96.1« 10 62.10 96.2« 20 81.90 The resin according to the invention may be stripped by alkaline metals cyamides also.

These results show that it is difficult to elute resin with 25 hydrochloric acid of a normality less than or equal to 4. On the other hand, an acidity of around 4 to 6 N makes -17it possible to recover the copper with a good yield, on the condition of using large volumes of solution. An acidity above 6 N would seem to be preferable.

Claims (8)

1. CLAIHS 1A process for treating solutions of lead chloride containing, as impurities, at least one of the metals silver, copper and bismuth, the process comprising the 5 following steps: a) contacting the solution with a cation exchange resin, the active grouping of which is a sulfhydryl group; and b) recovering the lead from the solution resulting from 10 step a).

2. A process in accordance with Claim 1, in which all the copper is reduced to the Cu + state prior to step a).

3. A process in accordance with Claim 2, in which the redox potential of the solution prior to its passing over the resin 15 is brought to a value less than or equal to 0 with respect to the saturated calomel electrode.

4. A process in accordance with any of Claims 1 to 3, in which the redox potential is broughtto, and maintained at during the whole duration of step a), a value between 520 20 and 560 millivolts.

5. A process in accordance with any of Claims 1 to 4, in which the temperature of the solution is maintained during step a), at a value between 60°C and boiling point. -196.

6.A process in which step in accordance with any of Claims 1 to 5, b) comprises an electrolysis process.

7. A process in accordance with any of Claims 1 to 6, and further comprising the following step: 5 c) elution of the resin saturated with impurities, using a 5 to 12 N solution of hydrochloric acid.

8. A process substantially as hereinbefore described with reference to the examples.